Arginineamides are known to have anti-thrombotic activities and are expected to be used as anti-thrombotic agents (please refer to Japanese Patent No. 1382377). However, it is very difficult to obtain a solution containing any of arginineamides at high concentration due to poor solubility in water and therefore any of these compounds is not suitable for applying as the injection containing it at high concentration.
An object of the invention is to provide a method for improving the solubilities of arginineamides so as to apply as the injections containing them at high concentration.